You can also view a list of all available packages and their description by running:

# pkg rquery "%n (%c)"

Note that "packages" is used for FreeBSD style command line tools, while "plugins" is used for GUI-enhanced additions in our nomenclature, something that pfSense also calls "packages". We just don't want to keep confusing people about whether we have a package that has a GUI component. It makes communication and expectations easier to manage.

Some packages are good candidates for plugins, but plugins are largely a community thing from our perspective so that they need to be worked on in order to become a part of the plugin system for others to be installed. In the case of vnstat this has been asked a few times, but nobody stepped up yet. We do have a similar solution now with NetFlow/Insight that might suffice for some.

They run with a script in the background every 5 seconds to update the rackmount LCD stats (Down/Up Speed , OnPeak/OffPeak usage).

Have you tried lcdproc? I've had a rackmount LCD in passthrough mode a while ago and it worked with one of the lcdproc drivers. There's no plugin for lcdproc, but I have a FreeBSD 10.3 VM build environment and compiled lcdproc there. I just copied the files over to my opnsense machine and it worked beautifully.